I may not be 100% impartial ;-), but I’m pretty sure this is not going to be the case. Apollo already supports more of the GraphQL spec than Relay does today!! In fact, Apollo is the only GraphQL client I know of that supports the full GraphQL spec, and it’s moved faster than Relay in adopting new features of GraphQL (see susbcriptions for example). The main reason is that Apollo is an open-source project driven by a community where everyone can contribute and influence the direction of development, whereas Relay is a project completely owned by Facebook, developed for Facebook’s needs. It just happens to be open-source as well. I guess time will tell who is right :)
Great post by the way!